This invention relates generally to combinations of oil-soluble additives for lubricating oils.
Zinc dialkyldithiophosphates (ZDDP) are widely used as lubricant additives. The principal disadvantages of these compounds are that an ash residue is produced by the zinc as the additive is consumed, and that phosphorus is known to affect the efficiency of catalytic converters in motor vehicles, thereby causing emissions problems. Dithiohydantoin compounds are disclosed in European Patent Application No. EP 0 728 747 A1. However, the compounds are not within the scope of the present invention, and moreover, are disclosed only for pharmaceutical applications.
The problem addressed by this invention is to find improved oil-soluble additives for lubricating oils.
The present invention is directed to a composition comprising:
(a) from 1% to 99% of at least one compound of formula I: 
xe2x80x83wherein W represents O, Sxe2x80x94A2, or two groups, R3 and R4; bonds a and b are single or double bonds, provided that one of a and b is a single bond and the other is a double bond; c is a single or double bond, and d is a single bond, double bond, or two single bonds, provided that d is a single bond when c is a double bond, d is not a single bond when c is a single bond, and W is R3 and R4 when d is two single bonds;
A1, A2, B1 and B2 are independently hydrogen, alkyl, alkenyl, aralkyl or one of the groups depicted in Scheme 1: 
xe2x80x83provided that B1 is absent when b is a double bond, B2 is absent when a is a double bond, A1 is absent when c is a double bond and A2 is absent when d is a double bond; and provided that A2 or B2 is not aralkyl when W is O or Sxe2x80x94A2;
R1, R2, R3 and R4 are independently hydrogen, alkyl, alkenyl, aryl or aralkyl; or R1 and R2, or R3 and R4, combine with the carbon atom to which they are attached to form an alkyl or alkenyl ring; Y is O or S; Z is O, S or NR9; m is 0 when bond e is a double bond and 1 when e is a single bond; n is 1 when bond f is a double bond and 2 when f is a single bond; R5 is C(Y)ZR7, hydrogen or C1-C4 alkyl; R6 is hydrogen or C1-C4 alkyl; R7, R8, R9, R10, R11 and R12 are independently hydrogen, alkyl, alkenyl, aryl or aralkyl;
provided that at least one of A1, A2, B1 and B2 is present and is not hydrogen; and
(b) from 1% to 99% of at least one dithiophosphate.
The present invention is further directed to a composition comprising a lubricating oil, from 0.05% to 15% of a compound of formula I, and from 0.01% to 10% of a dithiophosphate; and to a method for improving the anti-wear and anti-corrosion characteristics of a lubricating oil by adding from 0.05% to 15% of a compound of formula I, and from 0.01% to 10% of a dithiophosphate.
All percentages are weight percentages based on the entire composition described, unless specified otherwise. An xe2x80x9calkylxe2x80x9d group is a saturated hydrocarbyl group having from one to twenty-two carbon atoms in a linear, branched or cyclic arrangement, and having from 0 to 2 oxygen, nitrogen or sulfur atoms. Substitution on alkyl groups of one or more halo, hydroxy, alkoxy, alkanoyl or amido groups is permitted; alkoxy, alkanoyl and amido groups may in turn be substituted by one or more halo substituents. In one preferred embodiment, alkyl groups contain from one to twelve carbon atoms and from 0 to 1 oxygen, nitrogen or sulfur atoms; in another preferred embodiment, alkyl groups contain from 12 to 22 carbon atoms, and more preferably, no heteroatoms. An xe2x80x9calkenylxe2x80x9d group is an xe2x80x9calkylxe2x80x9d group in which at least one single bond has been replaced with a double bond. An xe2x80x9calkanoylxe2x80x9d group is an alkyl group linked through a carbonyl group, e.g., an acetyl group. An xe2x80x9carylxe2x80x9d group is a substituent derived from an aromatic compound, including heterocyclic aromatic compounds having heteroatoms chosen from among nitrogen, oxygen and sulfur. An aryl group has a total of from five to twenty ring atoms, and has one or more rings which are separate or fused. Substitution on aryl groups of one or more halo, alkyl, alkenyl, hydroxy, alkoxy, alkanoyl or amido groups is permitted, with substitution by one or more halo groups being possible on alkyl, alkenyl, alkoxy, alkanoyl or amido groups. An xe2x80x9caralkylxe2x80x9d group is an xe2x80x9calkylxe2x80x9d group substituted by an xe2x80x9carylxe2x80x9d group. A xe2x80x9clubricating oilxe2x80x9d is a natural or synthetic oil, or a mixture thereof, having suitable viscosity for use as a lubricant, e.g., as crankcase oil in an internal combustion engine, automatic transmission fluid, turbine lubricant, gear lubricant, compressor lubricant, metal-working lubricant, hydraulic fluid, etc.
A xe2x80x9cdithiophosphatexe2x80x9d is any compound having a dithiophosphate group, preferably a dithiophosphate ester group {(RO)2P(S)Sxe2x80x94, where the R groups are the same or different alkyl, aryl, aralkyl or alkenyl groups}, for example, a dialkyldithiophosphate group, a diaralkyldithiophosphate group, or a combination thereof. Examples of dialkyldithiophosphates include, but are not limited to, S-alkanoyl dialkyldithiophosphates, S-alkyl dialkyldithiophosphates and ZDDP. The term xe2x80x9cZDDPxe2x80x9d refers to a zinc dialkyldithiophosphate having the structure 
wherein RA, RB, RC and RD independently represent C1-C22 alkyl groups. Preferably, alkyl groups are primary or secondary alkyl groups. Preferably, alkyl groups are C2-C12 alkyl groups, more preferably C2-C8 alkyl groups, and most preferably C3-C6 alkyl groups.
In formula I and Scheme 1, the letter a, b, c, d, e or f represents the total bonding between the atoms adjacent to each letter, e.g., when xe2x80x9caxe2x80x9d represents a single bond, the sulfur atom and ring carbon to which it is attached are connected by a single bond. These letters are used in formula I to indicate that the compound may exist in different tautomeric forms, e.g., when the sulfur shown in formula I is substituted, i.e., B2 is present, a is a single bond, b is a double bond and B1 is absent, as will be understood by one skilled in the art. In the substituent groups of Scheme 1, e and f indicate whether the bond between the adjacent carbons is a single or double bond, which is determined by the alkylating agent used to introduce the substituent, as described hereinbelow.
It is preferred that at least one of A1, A2, B1 and B2 is present and is not hydrogen or methyl. It is preferred that if the only one of A1, A2, B1 and B2 which is present, and is not hydrogen, is alkyl, then it is C8-C22 alkyl, more preferably C16-C22 alkyl, i.e., it is preferred that any alkyl group attached to nitrogen or sulfur is in one of the aforementioned ranges. It is also preferred that A1, A2, B1 and B2 are independently hydrogen or one of the three groups depicted in Scheme 1. It is also preferred that W is R3 and R4, and c is a single bond. It is also preferred that W is R3 and R4, c is a single bond, A1 is hydrogen, and B1 or B2 is one of the groups depicted in Scheme 1.
Preferably, Y and Z are O, e is a single bond, m is one and R5 and R6 independently are hydrogen or methyl. Preferably, R7 is alkyl. In one aspect of the invention, a tetraalkylimidazolidinethione (TAIT), or an imidazolidinethione having from one to three alkyl groups, is alkylated with an acrylate ester to produce a compound having a xe2x80x94CHR5CHR6C(O)OR7 group, as shown below for an alkyl acrylate, resulting in R5xe2x95x90R6xe2x95x90H and R7xe2x95x90alkyl. Reaction with methacrylate or crotonate esters, resulting in R6xe2x95x90CH3 or R5xe2x95x90CH3, respectively, also is possible. If R1, R2, R3 and R4 are all methyl, the TAIT is known as TMIT. 
The extent of N-alkylation versus S-alkylation varies with the identity of the R groups on the imidazolidenethione ring and with the alkylating agent, as shown below in the Examples.
In another aspect of this invention, a TAIT or an imidazolidinethione having from one to three alkyl groups is alkylated with an alkyl propiolate to produce a compound in which the ester side chain has a carbonxe2x80x94carbon double bond. In another aspect of this invention, a TAIT or an imidazolidinethione having from one to three alkyl groups is alkylated with an imine, CR11R12xe2x95x90NR8. Preferably, R8 is C12-C22 alkyl. Preferably, R11 and R12 independently are alkyl or hydrogen. In a preferred embodiment of the invention, CR11R12xe2x95x90NR8 is a formaldehyde imine, CH2xe2x95x90NR8. In another aspect of this invention, a TAIT or an imidazolidinethione having from one to three alkyl groups is alkylated with maleic or succinic anhydride to produce a compound having a xe2x80x94C(O)CHxe2x95x90CHC(O)OH or xe2x80x94C(O)CH2CH2C(O)H side chain, respectively, with alkylation occurring mainly on the sulfur. In another aspect of this invention, a TAIT or an imidazolidinethione having from one to three alkyl groups reacts with an isocyanate or isothiocyanate to produce a compound having a xe2x80x94C(O)NHR10 or xe2x80x94C(S)NHR10 group, respectively. Preferably, R10 is aryl, alkyl or aralkyl, more preferably aryl or C8-C20 alkyl.
In one embodiment of the invention, the group ZR7 in a xe2x80x94CHR5CHR6C(Y)ZR7 side chain or a xe2x80x94CHxe2x95x90CHC(Y)ZR7 side chain contains a thioethyl group, i.e., a group having the structure xe2x80x94CH2CH2Sxe2x80x94, where one of the CH2 and the sulfur is attached to the C(Y) functionality and the other is attached to an alkyl, alkenyl or aralkyl group. For example, ZR7 can be OCH2CH2Sxe2x80x94R, where R is alkyl, alkenyl or aralkyl; when Y is O, and R5 and R6 are H, the side chain is xe2x80x94CH2CH2C(O)OCH2CH2Sxe2x80x94R.
In one embodiment of the invention, A1, A2, B1 and B2 are independently hydrogen or one of the groups depicted in Scheme 2: 
Preferably, Y and Z are O, e is a single bond, m is 1, and R5 and R6 independently are hydrogen or methyl. Preferably, R8 is C12-C22 alkyl. Preferably, A1, A2, B1 and B2 are independently hydrogen or one of the groups depicted in Scheme 3: 
Preferably, a synergistic combination of lubricant additives comprises from 10% to 90% of a compound of formula I and from 10% to 90% of a dithiophosphate, more preferably from 20% to 80% of a compound of formula I and from 20% to 80% of a dithiophosphate, more preferably from 25% to 75% of a compound of formula I and from 25% to 75% of a dithiophosphate, and most preferably from 40% to 60% of a compound of formula I and from 40% to 60% of a dithiophosphate. In one embodiment, the synergistic combination contains less than 10% of any other ingredient, more preferably less than 5%, more preferably less than 1%, and most preferably is substantially free of other ingredients. In another embodiment of the invention, other additives typically used in lubricating oils are present in the composition. Such additives include, but are not limited to, dispersants, detergents, antioxidants, antifoamants, friction modifiers, seal swell agents, demulsifiers, viscosity index improvers and pour point depressants. In a preferred embodiment of the invention, from 0.05% to 10% each of a compound of formula I and a dithiophosphate are added to a lubricating oil, more preferably, from 0.1% to 5% each, more preferably, from 0.1% to 2% each, more preferably, from 0.2% to 2% each, more preferably from 0.2% to 1% each, and most preferably, from 0.2% to 0.6% each. Preferably, the ratio of the amount of the compound of formula I to the amount of a dithiophosphate is from 1:9 to 9:1, more preferably from 1:4 to 4:1, more preferably from 1:3 to 3:1, and most preferably from 2:3 to 3:2. Preferably, the dithiophosphate is a dialkyldithiophosphate, most preferably a ZDDP. A lubricating oil is a natural or synthetic oil, having suitable viscosity for use as a lubricant, or a mixture thereof.